Fibrous composition containing filler and binder substances and process of making them



Patented Mar. 14, 1933 UNITED STATES PATENT OFFICE EARL P. STEVENSON, OF NEWTON,

MASSACHUSETTS, ASSIGNOR TO THE RICHARDSON COMPANY, OF LOCKLAND, OHIO, A

CORPORATION OF OHIO FIBROUS COMPOSITION CONTAINING FILLER AND BINDER SUBSTANCES AND PEOCEQB OF MAKING THEM Application filed April 6,

No Drawing.

My present invention is concerned with the manufacture of fibrous compositions and articles containing organic binders and mineral or other fillers, wherein the fiber distribution and construction is characteristically that of a paper mill product, and is more particularly related to the preparation of a watery pulp in which fiber, binder and filler are intimately associated. Broadly, in the practice of my invention I employ a basic principle which was set forth in United States Patent No. 1,771,150, of July 22, 1930. This principle applies to the manufacture of pulps suitable for formation on a screen by a method which comprises first pre-associating a binder substance and a fibrous material while the fibers are not in water suspension in the sense of constituting a pulp, and after such pre-association has been produced, then suspending the fibrous material and the associated binder substance in water sufiicient to act as a circulating medium, and refining the stock for felting.

It has been found possible to produce a relationship or pre-association between fibers and a binder substance even in large amounts of the latter, which pre-association is not wholly destroyed in any subsequent treatments which the fibrous material receives, such as in beating or J ordaning, to prepare them for felting upon a screen. The stability of the association is apparently a residual function of the pre-association of the fibers and the binder substance.

In a co-pending application, Serial No. 468,454, filed July 16, 1930, in the names of Stevenson and Buron, there has been described and claimed a procedure employing the same general principle, but directed to the production of articles in which a synthetic resinous material is associated with the fibers." My present invention is distinguished in point of novelty from the patent and application hereinabove mentioned, by the manner in which the filler is incorporated, and by the adhesive relationship here obtained between an organic binder and a mineral filler, whereby new and useful results are produced.

1931. Serial N0. 528,248.

various kinds of fibers, binders, and filler materials, varying in their combinations with the specifications ished product. Generally I prefer to use the conventional paper making stocks, such as kraft, sulphite, soda, rag or ground wood pulps, deriving these, if desired, from waste,

materials, such as old news, mixed. apers, sulphite clippings, and old rags. Wit vegetable fibers may be combined various percentages of animal fibers, such as wool, or of mineral fibers, such as asbestos.

Likewise, my process is not restricted to the use of any one type of organic binder. Asphalts, bitumens, pitches, natural resins, such as rosin and shellac,

ments; increased dielectric strength may be obtained with particular fillers; special molding properties with others, and-the like.

The object of my invention is the production of a pulp of feltable fibers in suspension in a circulating medium with which a binder substance is associated, together with a filler substance. Another object of my invention is the production of a novel type of association between theseveral substances which go to make up my pulp.

Still another object of'my invention is the I provision of a new and useful process for the employment of fillers in pulps which contain binder substances. Still another object of my invention is the production in felted articles of enhanced qualities derived in part from the physical association of the 'ingredients which go to make up the pulp. These and other objects of my invention which will be set .forth hereinafter, or will required of the finand many kinds. I of synthetic resins can be employed. The. be thermo-plastic 50 My present process permits of the use of be apparent to one skilled in the art upon 100 as a one-sta e creosol-forma readmg' these specifications, I accomplish by that certain process and series of manipulations, and in that product of which I shall now describe an exemplary embodiment. The particular objectives and advanta of my process ma be illustrated with re erence to the manu acture of sheets, boards or formed pulp products containing as the binder a synthetic resin such for example, ldehyde resin. Withinthe c assification of synthetic resins I would broadly include the condensation roduct of an aldehyde, the .polymer of a ydrocarbon derivative, or the product of the reaction between a olyhydroxy alcohol and an organic acid. his group comprises individual resinous substances of widely differing properties, and the adaptatlon of any one in particular must take into account its propertles with reference to the conditions 0 use in the present process and: the roportion desired 1n the finished roduct. Eor example, the synthetic resins 'fier in point of time and temperature for conversion under heat into their infusible and/or insoluble form. Generally those having a relatively long curing time are requlred when elevated temperatures are employed in the process of drying the resinous gulp product, as, for example, in passing s eets over the heated drying drums of a paper machine. Combinations of these various synthetic resins in a felted fibrous structure I can be converted under heat and pressure into dense, so-called laminated phenolic products posessing great tensile strengt-h, desirable electrical properties, resistance to moisture, and to the action 'of organic solvents and dilute acids.

Heretofore the base stock for laminated phenolic products has been made by saturating special papers, generally kraft or an absorbent cotton or purified wood cellulose paper, b passing it through a resin solution. The solvent is then evaporated by means of heat, leaving the resinous matter coated upon and partially incorporated in the paper. From the apers so treated the various laminated pro nets of this industry have been made by stackingrtogether either sheets or shapes out there om to make a roduct of the desired thickness and cured tween steam-heated platens in a hydraulic press at temperatures ranging from to 200 centigrade, and under pressures of 1000 to 3000 pounds per square inch.

The present invention is concerned with a new method for securing a felted fibrous structure containing resin. The product can be cured and pressed in equipment, and by the procedure now followed in the handling of paper sheets coated and partially saturated with resin. In other respects the roduct is quite novel, as will be understood om what follows.

The method consists essentially ing together in a suitable mixer a mass of wetted cellulosic fibers and. a liquid or semi liquid resin, referabl reduced to this state by means of eat. When the cellulosic material, generallyK paper or a pul has been sufliciently bro en, that is, de brated, .by the action takin place in the mixer, and the resin binderiasbeen uniformly incortprorated or distributed throughout the wet brous mass, more water is added. With continued mixing and heating, the fibers slowly absorb the water and the adhesive masses break down into a watery pulp which, with further refining as in a beater followed by Jordaning, can be reduced to the consistency re uired for forming on a cylinder screen, ourdrinier wire, shape mold, or other pulp-forming device. In this manner sheets, boards or formed articles can be economically manufactured by conventional equi ment. Essentiall this is the process set orth in the co-pen 'ng application of Stevenson and Buron, Serial No. 468,454 referred to hereinabove.

Advantages inherent in this method, as compared with the processes of saturating paper and other webs with synthetic resins, which are at present in general use, com-- prise: (1) no solvents are required; (2) the resin is more uniformly distributed with res t to fiber surfaces; (3) sheets of any deslred thickness can be made with resulting economies in pressing and molding; (4) cheaper fiber stock can be used, such, for example, as waste papers; (5) uncured scrap from trimming and the cutting out of irregular shapes can be completely salvaged; (6) less resin is r uired to secure the same degree of strength, density, and molding properties. All of these advanta es are of practical importance.

n workin with synthetic resins as well as other bin ers, I have carried this process one step further. It is now proposed to incorporate in compositions of this character, filler substances which are of non-fibrous or substantially non-fibrous character. A result of certain character may be obtained by mixing mineral fillers or the like with the pulp as it is being beaten or refined, as by adding suchfillers to the paper mill beater. This has its disadvantages, however, residing primarily in that filler substance added to the beater is not homogeneously distributed throughout the body of the pulp, and insofar as it is brought into suspension therein, does not exhibit to any practical extent a stability of association therewith. It is therefore incompletely retained upon the screen when the fibers are felted together to form the finished product. As a consequence, much of it is lost, and the final product becomes nonuniform and may have a distinctly striated character.

By my present process I provide a ractical means for incorporating mineral era with the synthetic resin in my exemplary embodiment, wherebiy the fillers become umformly incorporate in the finished sheet, board or formed-up pulp, and are largely retained in the pulp as it IS being de-watered and formed up. Broadly, in the ractice of my inventiominstead of adding t e filler to the beater, I add the filler to the mixer wherein the binder is in an adhesive state, and wherein there is relatively so small a content of moisture, if any, as will not be efiective in preventing the initial adhesion to, and incorporation of the filler 1n the body of the binder. I prefer thoroughly to incorporate m filler with the binder m a liquid or semiliquid state before I incorporate the fibrous material therewith. By mixing my filler, usually substantiallg) dr with the binder substance, I can uni rm y distribute the filler throughout the binder; and when I subsequently make my premix, i. e., when I add my wetted fibrous material to the mixer and incorporate it with the binder, and when I subsequently beat ofi the fibers and distribute them in a circulating medium, I find that the binder has the same relationship to .the fibrous material in the finished pulp as hitherto, namely, it exists in minute, uncoated particles in stable relationship with the fibers; but it differs from binders hitherto employed by me in that it contains within its body and within the bod of such particles as now constitute the bin er, a substantial quantity of a mineral or other non-fibrous filler. In this way the filler is uniformly distributed, and is in a substantial degree adhesively associated with the binder, whereby, when the pulp is finally formed up, the filler material is very well retained therein.

With certain fillers andbinders practically the same end result may be obtained by adding the filler to the mixer with, or immediately after, the wetted fibrous material, depending, I believe,-in point of theory, uponthe degree of relative ease with which a particular mineral filler is wettedby water or by the binder. If the filler, however, is one that is preferentially wetted by water it will not readily enter into an-adhesive rela tionship to the binder and may ap ear in the final pulp in suspension quite in ependent of the binder. In such case the final result may be quite the equivalent of adding the filler to the beater at the pulping or refining stage. If there is a contact relationship between the filler and the binder in the finished pulp under these circumstances it appears to exist largel in a sporadic adhesion of particles of filer to the globules or fragments of binder which are, in considerable measure, in adhesive contact with the fibers in the final pulp."

With certain binders I have 'been ablesto incorporate by this procedure an amount of in weight to that of the binder,

fit and 'su ntially to retain both the binder and the filler in the stock when de-watered and formed upon a screen. This is indi cated, however, by way of exam 1e, without implying an upper limit for fi er incor oratlon. The filler need not be added ry to the binder material, but may be added wet if desired, and the mixing continued to the point of driving out the greater part if not all of the water, prior to the addition of the fibrous material. The water should be driven out when following 'my preferred procedure, at least to the extent of bringing about an adhesive association between the filler and the binder. When mixing together filler and binder, it is not essential that any water be preserved in the mixer,

as it is with the fibrous material in an advantageous rocedure; since the combined binder and er appears to act in the subsequent process steps for the formation of the pulp, substantially as a simple binder. Thus, while it is advisable not to carry on the mixing of the binder (with or without filler) and the fibrous material to the point of driving out all of the water in the mass, so as to preserve the avidity of the fibers for water, to preserve an incompletely coated condition of the fibers, and resumably to permit the formation of hy ro-cellulose as the fibers are being beaten to form a pulp, the relationship of the filler to the binder is preferably that of a completely coated condition of the filler which is' not thereafter alleviated.

In the instance of premixing a synthetic resin compounded with a mineral filler and cellulosic fibers, certain desirable properties are realized in the molding of pulp articles under heat and pressure. For example, a board so made, and prior to the curing of the sflynthetic resin, has the property of plastic ow even with relatively low percentages of binder. The lower limlt can not be specified as it will vary with difierent resins; but properties of plastic flow have been noted in formed pulps made under my process, in which the resin constitutes less than 40% of the'dry pulp by weight. Webs of fibrous material, such as paper or the like, which have been coated and/or saturated with a synthetic resin, may be pressed and cured, but they do not exhibit to any markeddegree the properties ofplastic flow under heat and pressure. If any substantial deformation is attempted, the web puckers or ruptures, and the desired result is not perfectly obtained. With premixed pulps, if the binder is inexcess of the fibrous material, the quality of true plastic flow has been noted; but where the binder'is relatively low in amounts, this property has not been perfectly developed. In a pulp made b smy process, however, thefiller serves to ubna cate the m permittin a certain degree of flow in the bers and a so facilitating the 3 flow of the resin. iEvenwith relatively low amounts' of binder hereinabove referred to, I have found that my material is truly heatplastic, and will flow and fill all of the intersticesof a complicated mold. Thus, in pressing under heat, the pressure is equalized, a much more homogeneous article results, and the final product is free of puckers ruptures, knit l nes, and the like.

iet another advantage inherent in this use of a mineral filler is increased mechanical strength in the pressed and cured articles made from this new resinous ulp. The advantages, derived from t e use of mineral fillers in resinous pulps, made in accordance with my process, are not restricted to binders of the synthetic resin type, but are also to be noted in the use of other binders.

My process is, of course, of especial importance in the field of molded compos1- tions containing synthetic resins, because here it is advantageous for a number of reasons, not the least of which is economic, to kee the amount of binder relatively low, an to secure the mechanical reinforcement of a felted fiber structure. The range and u utility of products which can be molded from sheeted fibrous stock containing synthetic resins has been greatly extended by my invention.

As an example of a procedure in working with synthetic resins I may state the following: An exemplary resin suitable for my process may be prepared as follows:

Cresylic acid 39 pounds Phenol 10 pounds Formaldehyde "47 pounds Ammonia 4 pounds All of the ingredients are mixed together and heated in a steam-jacketed vacuum kettle equipped with a condenser, to a temperature of about 90 0., where the reaction starts and the temperature rises rapidly to 110 C. After about 20 minutes the reaction subsides whereupon heat is applied and the temperature maintained at 100 C. for about 40 minutes. Vacuum is then applied and heating continued. This removes the water originally present in the formaldehyde and that formed by the condensation reaction. Heating is continued and the temperature slowly raised to 110 C. and held at this temperature until the resin has been advanced to the proper stage, as shown by the hardness of the resin on cooling and by its rate of curing.

The rate of curing of the resin is determined by'a hot plate test conducted as fol- 65 lows: A small amount of the resin is worked imately 90 seconds, and becomes rubbery in.

approximately 250 seconds by the hot plate test.

The type of resin used is dependent upon the time and temperature used in drying the finished aper or board and the resin just described is an example of a resin suitable for use in heavy board which is to be dried in a Coe dryer or other apparatus which maintains atem erature between 100 and 125 0., under whic condition the board becomes dry in approximately 2 hours.

For paper which is to be air-dried or dried at lower temperatures faster curing resins, such as those made with h' her percenta es of phenol, may be used. gare must be ta en, however, to select a resin which will not become cured during the drying of the paper to the extent that it no longer has plastic flow under the heat and pressure condition used in molding.

This resinous material is placed in a. suit able mixing or kneading machine, such as the well-known Werner-Pfleiderer mixer, and under the influence of heat is brought to a semi-liquid or plastic condition. "The desired quantity of'mineral or other filler, say slate dust to the amount of 20% by weight of the synthetic resin, is added thereto. As hereinabove explained, the nature and uantity of the mineral or other filler may e widel varied, and it is not necessary to descri e a separate procedure with Varying fillers or varying amounts thereof. The filler may be added wet or dry The rotation of. the mixer blades is started, and in either instance mixing is carried preferably to the point of forming a homogeneous distribution of the filler material in the binder. If the filler material has been added wet, it is advantageous to continue the mixing until the moisture has been driven out, and until the filler is not only com letely incorporated in the body of the binder, but also in adhesive contact relationship therewith in all its parts. The filler will preferably be in a completely coated condition.

After the incorporation of the filler into the binder material, the fibrous material can be readily molded, as hereinabove described, a quantity of fiber can be used such which has been previously wetted with that the resulting pulp will have use 01- lowing composition when computed upon the air-dry basis:

Resin 50 per cent Fiber 40 per cent Mineral filler per cent A suitable fiber furnish is one comprising equal weights (air-dry basis) of rag half stock and sulfite clippings. The use of some rial have been thoroughly mixed, but preferably before the water has been driven out of the mass under the influence of heat, and while the fibers have substantially an incompletedly coated condition and an avidity for water, the resultant mass in the mixer is broken down to a semi-pulp by the addition of more water. This semi-pulp may then be transferred to a beater and beaten into a true pulp in which the fibers are fitted for felting, and are suspended in a quantity of water sufiicient to act as a circulating medium. This pulp may be refined and/or diluted as desired, and may be formed up upon the screen of a paper makin machine or other pulp forming device. n it the binder exists in minute, uncoated particles in stable and partial adhesive contact association with the fibers, with the binder particles themselves substantially containing the filler materials.

The formed and dried pulp will have the characteristics,under heat, of plastic flow, and can be formed up under heat and pressure and cured to cause the resin to assume an infusible and/or insoluble condition. Prior to the treatment under heat and pressure, the resin should be largely in a secondary or incompletely cured condition, and any scrap which is the result of trimming or cutting the blanks forthe pressing or molding operation, may be re-used in subsequent batches of stock, preferably introduced at the premixing stage, or it can be shredded and used as a molding compound.

In working with other binder materials substantially the same procedure may be followed. Thus, to an asphaltic substance such, by way of example, as those described in United States Patent No. 1,771,150, I may add in the mixer a desired quantity of a mineral filler, such as the slate dust or finely ground silica, diatomaceous earth, or the like, and after thoroughlyincorporating the two together, treat the combined mass as a binder, subsequently following through a procedure like that of the Stevenson and Buron Patent No. 1,771,150.. With other increase in mo binders than synthetic resins, and particularly with non-porous fillers, an equivalent dability results from the filler incorporation, and, of course, with these other binders I achieve the other objects of my invention: substantially complete retention of the filler, and homogeneous distribution thereof.

Since the primary object in adding a mineral' filler to a composition of synthetic resin and a paper making fiber is to secure improved molding properties under heat and pressure for a minimum amount of resin contained therein, the pro er selection of filler and amount thereo is important. While for a given composition this factor can only be determined by experimentation, the use of absorbent materials, such as diatomaceous earths, is not recommended. Materials such as 200 mesh silica, finely ground felds ar and paper makers clay will enerally e found satisfactory. When c0 or is desired the filler may consist in part ofpigments or lakes.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A fibrous pulp in water suspension in association with a binder substance in particle form, the binder particles containing filler materials in substantially homogeneous distribution therein.

2. A pulp of paper making fibers in suspension in a circulating medium, containing binder particles in substantially homogeneous distributon, the said binder particles containing filler particles in substantially completely coatedcondition.

3. A pulp of feltable fibers in water sus pension, and containing in stable association therewith a dispersed synthetic resin in combination with a pigmented mineral filler.

4. A pulp of feltable fibers in stable association with a dispersed synthetic resin containing a pulverulent mineral filler, and further characterized by freedom from uncombined mineral filler.

. 5. An uncoated composition of felted fibers containing in its interior and-within the confines of its surface enough thermoplastic material to flow outwardly upon fusion under heat and pressure so as to form a continuous film wholly encasing the fibers and a mineral filler uniformly distributed throughout said composition and dispersed in said binder.

6.. An uncoated composition of felted fibers containin in its interior and within the confines of its surface enough synthetic resin in an incompletely cured stage to flow outwardly upon fusion under heat and pressure so as to form a continuous film wholly encasing the fibers and a mineral filler uniformly distributed throughout said composition and dispersed in said binder.

. 7. An uncoated composition of felted fibers containin in its interior and within the confines of its surface a synthetic resin in an incompletely cured state and a mineral filler, the particles of said filler being coated with and uniformly distributed in the resin material.

8. A molding composition comprising a structure of felted fibers and containlng within its confines and in intrafiber distribution a mineral filler associated, as herein described, with a synthetic resin suflicient in quantity to flow outwardly upon fusion under heat and'pressure to form a continuous encasing film.

9. A molding composition comprising a structure of felted fibers and containing within its confines and in intrafiber distribution a mineral filler associated, as herein described, with a synthetic resin sufiicient in quantity to flow outwardly upon fusion under heat and pressure to form a continuous encasing'film, and further characterized by the property of plastic flow under the conditions of molding.

10. A process of making a pulp which contains a binder and filler material, which comprises combining a filler material with the binder substance under conditions permitting an adhesive relationship between said substances, whereby the filler becomes completely coated with said binder, and associating the resulting binder with the fibrous material under conditions in which said fibrous material comes into adhesive contact with said binder material but is incompletely coated thereby, and subsequently dispersing the mass so formed in water to the extent of fitting the fibers therein for formation upon a paper machine screen.

11. A process of forming a pulp of fibrous material containing binder and filler substances, which comprises associating said binder and said filler substances under saturating conditions, and said binder and said fiber under non-saturating conditions, and subsequently dispersing the mass so formed in water suflicient to act as a circulating medium.

12. The process of making a pulp of fibrous material, binder and filler, which comprises associating said binder and said filler under saturating conditions, and said binder and said fiber under non-saturating conditions but suflicient to bring about an adhesive relationship between the two, afterwards breaking down the said adhesive condition by the step of adding water as herein described and then dispersing the product so formed in water and beating the fibers to fit them for felting.

13. The process of preparing a fibrous pulp containing a filled plastic binder, comprising thesteps of reducing said binder to a molten condition, incorporating therewith quantity of wetted fibrous material, mixing under conditions to dispersethe fibers, and thereafter adding to the mixer an additional amount of water sufficient to artially break up the adhesive masses of fiber and filled binder, while maintaining temperature conditions throughout to preserve the resin in a substantially uncured state.

15. That process of forming a feltable pulp containing binder and filler substances, which comprises dispersing a filler in a binder and subsequently causing the said binder to adhere to fibrous materials in a pulp in water suspension, said binder existing in minute particles in said pulp and containing said filler material in dispersion.

16. A process of making fibrous pulps which comprises associating fibers, filler materials, and a binder under conditions insuring a complete coating of said filler material by said binder, but an incomplete coating of said fibrous material by said binder,

and afterward dispersing the mass so formed in water, and beating the fibers'to fit them for felting.

17. The process of making a pulp of fibrous material, polymerizable binder, and filler material, which comprises introducing a polymerizable binder in a secondary or incompletely polymerized stage into a mixing devlce and incorporating therewith a filler material to'the extent of effecting a substantially homgigeneous distribution of said filler in said bin er, afterwards mixing with said mass wetted fibrous materials without completely coating the individual fibers thereof with said binder, adding water and mixin to form a semi-pulp, transferring said semipulp to a heater and beating the said semipulp to form a true pulp of feltable fibers with said binder and said filler in stable association therewith.

18. The process of making a pulp of fibrous material, synthetic resin and filler, which comprises mixing a filler material with said resin while in an incompletely polymerized stage to the extent of substantial homogeneous distribution, premixing the mass so formed with wetted fibrous material, and beating the resulting product to form a pulp.

a pulverulent filler, and then adding there- 19. The process of making a pul of fibrous material, synthetic resin and er, which comprises mixing a filler materlal with said resin in an incompletely polymerized stage to the extent of substantial homogeneous distribution, premixing the mass so formed with wetted fibrous material, and beating the resultant product to form a pulp, forming the said pulp upon a screen of a 10 paper machine, drying the formed product, and pol erizing the resin therein under heat an pressure.

20. The process of making a pul of fibrous material, synthetic resin and Her,

which comprises mixing a filler material with said resin in an incompletely polymerized stage to the extent of substantial homogeneous distribution, premixing the mass so formed with wetted fibrous material,

and beating the resultant product to form a pulp, forming the said pulp upon a screen of a paper machine, drying the formed product, and polymerizing the resin therein under heat and pressure in a closed mold, said polymerizing being accompanied by the plastic flow of said material to fill the interstices of said closed mold. I

Signed at Cambridge, in the county of Middlesex, and State of Massachusetts, this twenty-eighth day of February, 1931.

EARL P. STEVENSON. 

